2 verses have
serious
in Edition Clear Qur'an by Talal Itani / Ibrahim (Abraham)

14:6Moses said to his people, “Remember God’s blessings upon you, as He delivered you from the people of Pharaoh, who inflicted on you terrible suffering, slaughtering your sons while sparing your daughters. In that was a serious trial from your Lord.”

14:9Has not the story reached you, of those before you, the people of Noah, and Aad, and Thamood—and those after them? None knows them except God. Their messengers came to them with the clear proofs, but they tried to silence them, and said, “We reject what you are sent with, and we are in serious doubt regarding what you are calling us to.”